The 48-year-old actor shared a photo of Kruger on Sunday after the 40-year-old In the Fade star won Best Actress at the 2017 Cannes International Film Festival.
"YESSSSS," he captioned the picture with three heart emojis.
Kruger, who plays a grieving wife and mother in In the Fade, responded to Reedus' post in the comments.
"Omg !!!!!!!!!!!!! Babe !!!!!!!!" she wrote, adding several heart emojis.
Kruger's ex-partner Joshua Jackson also celebrated the actress' win online. He and Kruger split in July after 10 years of dating.
"Yes she Cannes. Having witnessed the integrity and dedication that you bring to every job, I'm over the moon to see you getting the recognition you deserve. Only question is what took 'em so long! CONGRATULATIONS, Josh #dianekruger," the actor wrote.
Reedus and Kruger co-starred in the 2015 movie Sky, and were linked in March after they were spotted kissing in New York. Reedus, who plays Daryl on The Walking Dead, shares 15-year-old son Mingus with ex-partner Helena Christensen.